WoTC Boxes will have the lowest proportional return because they have already risen so dramatically in the past five years.
For example, I would not expect the Base Set Unlimited Booster Box to 4x in the next 5 years. That would require a ~$30,000 increase, which would be insane. However, I would expect a lot of S/M, SW/SH, and S/V boxes to 4x in the next 5 years because moving from $150 to $600 is significantly easier. This is why buying sealed product at scale (i.e., 6-box cases at a time at below MSPR) has very little downside risk.
Regarding Base Set, I expect the biggest growth to always be with the 1st Edition Holos. It’s not to say that Pikachu or the starters won’t appreciate over time, but they are significantly more abundant due to how commons, uncommons, and rares were printed on the sheet and distributed via boxes and boosters.
I personally think a lot of Diamond & Pearl and Platinum era booster boxes are underpriced given their age and rarity. I also believe that the Lv.X. cards are underpriced in the current market, but demand for these cards is pretty (understandably) low.
I see growth potential for high-end vintage Japanese promos not released in English (e.g., PLAY campaign), cards limited by release (e.g., Art Academy, Design Contests), and trophies (e.g., Snap Cards, Battle Road and Winter Challenge prizes). I do think English vintage chase cards from the e-Reader and EX era (i.e., crystals, gold stars) will appreciate as well and are largely underpriced. When it comes to WoTC, 1st Ed > Unlimited in terms of collectibility and rarity. I would not recommend stocking up on low pop vintage cards with huge PSA 10 premiums, as the pop reports can (and do) increase regularly.
Hope this helps. More than anything, I would recommend finding what jives with you and then base a potential investment around that.